1. Field of Invention
The present invention relates generally to optical switches and more particularly to waveguide based optical matrix switches.
2. Discussion of Related Art
Fiber optic networks for transmission of optical signals have come into wide use for telecommunications and data communications in recent years. These fiber optic networks need a rapid, efficient and effective means for switching a channel from one path to another within the network. Several switching techniques and structures have been developed in recent years that are satisfactory for many applications for switching a single channel from one path to another. However, these are not entirely satisfactory for functioning as large cross connect switches.
Several cross connect switches using a waveguide matrix have recently been developed. A common problem of current waveguide based matrix switches is the decrease in power of an optical signal as it traverses each potential switch point. The light typically leaves the waveguide at the switch points and propagates (unguided) across the cross point and then back into the waveguide. The coupling of the light from one waveguide to another results in a notable power loss at each cross point. A number of switch structures of this type are disclosed in U.S. Pat. Nos. 5,699,462 and 5,960,131. In general, an optical signal must traverse between one and (2*N)xe2x88x921 points in an N*N matrix switch.
Accordingly, there is a need for an improved waveguide-based switch that decreases the cross point power loss.
It is a primary purpose of the present invention to provide a waveguide based matrix switch that overcomes the above problems of the prior art by decreasing the cross point power loss.
The present invention provides a cross-point switch in which generally orthogonal waveguides are relatively parallel at their mutual cross point. For example, one of two generally orthogonal waveguides can have a 45 degree jog about the cross point, while the other waveguide has a xe2x88x9245 degree jog about the cross point. Herein, for purposes of determining whether two waveguides are generally orthogonal, the general orientation of a non-straight waveguide is that of a least-squares-fit straight line for that waveguide. A controller controls coupling material between the crossing waveguides to control the optical coupling between the waveguides. In practice, the waveguides can be formed at opposing faces of respective substrates.
This can be accomplished by placing two planar substrates parallel to one another, and having optical waveguides on the confronting surfaces. In the embodiment described in detail, the elongated waveguides on one plane are generally orthogonal to those on the other plane, except that at the crossing points each waveguide has a 45xc2x0 jog in such a way that a short portion of both waveguides in a pair of waveguides are parallel at the crossing zone. While the waveguides appear to cross from a plan view perspective, they are spaced from each other. These parallel, spaced segments provide for the optical signal to transfer from the waveguide in one plane to the one it crosses in the other plane. Controllable coupling material is mounted between the parallel waveguide segments in the crossing zone. Switching of optical signals between the waveguides at the crossing zone is accomplished by applying an electronic or a thermal signal to the coupling material between the waveguides.
Other crossing angles are contemplated as well as are other ways to form the spaced waveguide planes with coupling material at the crossing zones.
As in the prior art, waveguides that are couplable at a cross point are generally orthogonal to facilitate routing and to minimize unintended coupling away from cross points. By providing that waveguides are parallel at mutual cross points, the present invention provides an increased coupling area. The increased coupling area improves power coupling between the waveguides while the coupling material is controlled to promote coupling. Thus, the present invention decreases the cross point power loss. Certain embodiments of the invention provide other advantages in addition to or in lieu of the foregoing.